The present invention relates to an improved getter panel for use in a heat exchange system utilizing aqueous fluids.
Aluminum and its alloys have been used extensively for the construction of solar absorber panels, heat exchangers and the like due to its strength, light weight and ease of fabrication. One known method for producing tube in sheet absorber panels etc., is the ROLL-BOND.RTM. method, disclosed in U.S. Pat. No. 2,690,002. ROLL-BOND.RTM. is a registered Trademark of Olin Corporation. Two aluminum sheets are welded together by hot rolling with a pattern of stop weld material disposed between the sheets. High pressure fluid is then introduced between the portions of the sheets which have not been bonded together due to the presence of the stop weld material so as to distend the non-bonded portions into a tubular form.
Panels made in the aforesaid manner are used extensively as heat exchangers in heat exchange systems. However, in heat exchange systems using aqueous heat transfer fluids, corrosion is often a problem. This is particularly true in multi-metal systems containing heavy metals such as copper and iron which are often used in systems to make pipes, storage tanks, auxiliary heat exchangers and the like. Heavy metal ions will be present in aqueous heat exchange fluid due to the normal corrosion of the aforesaid elements in the heat exchange system. Since the electrode potential of aluminum is lower than that of the heavy metal, plating out of the heavy metals on cathodic areas of the aluminum panels results in the formation of local galvanic cells. Such cells promote rapid "pitting" or "pinholing" of the aluminum panels with the end result being leakage.
In order to prevent corrosion of the aluminum heat exchangers used in the heat exchange system, it has been known to provide the inner surface of the passageways with an oxide coating. However, this method has not been found satisfactory in completely precluding pitting corrosion. Another method used to produce aluminum panels was to clad an aluminum-zinc alloy sheet to a core sheet of an aluminum alloy and then join two such prepared sheets together. In such a system, the core sheet of aluminum is protected by sacrifice of the aluminum-zinc alloy cladding. Such a method has been found to be complex and costly due to the fact the two sheets must be bonded together before roll bonding. More importantly, since it was necessary for the sacrificial aluminum-zinc alloy to be on the inner surfaces, corrosion occurred at the bonded portions thereby resulting in penetration down the bonded interface and leakage of the heat transfer fluid. Protective claddings also only provide limited protection since they are consumed by corrosion leaving an unprotected core surface.
Another known method of producing tube in sheet panels is disclosed in U.S. Pat. No. 3,650,005. In this case, two aluminum sheets are welded together by hot rolling with a pattern of zinc or zinc alloy mixed with a solvent and a known stop weld material containing graphite disposed between the sheets. The sheets are then annealed and the zinc or zinc alloy is diffused into the interior of the aluminum to form an aluminum-zinc alloy layer. This method has been found to be ineffective since graphite, which is a strong cathodic depolarizer, causes electro-chemical corrosion in contact with aluminum in the presence of water.
While some non-corrosive stop weld materials have been produced which are free of graphite, such as that disclosed in U.S. Pat. No. 3,994,753, it is clear that it would be of considerable advantage and highly desirable to remove the heavy metal ions from the heat exchange fluid as aforesaid before they come into contact with the aluminum solar panels or the like.
Accordingly, it is a principal object of the present invention to provide a method for removing corrosive elements particularly heavy metal ions from a heat exchange system.
In is a particular object of the present invention to provide a "getter" in heat exchange system.
It is still a further object of the present invention to provide improvements as aforesaid which are inexpensive to utilize.
Further objects and advantages of the present invention will appear hereinbelow.